1. Technical Field
The present invention relates to an apparatus equipped with an optical band filter capable of changing its center wavelength and band width, and a method of controlling the same.
2. Background Art
A technique in which additional optical wavelength multiplexers and optical wavelength dividers are successively installed so as to cope with the communication demand while maintaining the communication state is disclosed in International Republication No. WO02/011337. This technique is composed of a master rack and slave racks. A certain number of optical wavelength signals are processed and managed by the master rack in the early operation, and then additional slave racks are installed one after another by coupling them to the master rack so as to cope with the increasing demand for the wavelength signals.
A related optical wavelength dividing multiplexing device is explained hereinafter with reference to FIGS. 5 and 6. FIG. 5 shows an optical wavelength multiplexing device, and FIG. 6 shows an optical wavelength dividing device. In the optical wavelength multiplexing device in FIG. 5, optical signals having different wavelengths output from OS1s p-1-p-k are individually compensated for their dispersion by DCMs 2p-1-2p-k, and become an optical wavelength multiplex signal of λ1-λk at a CPL 3p. The optical wavelength multiplex signal λ1-λk is collectively compensated for dispersion by a DCM 5p and amplified by an AMP 6p to compensate for the insertion loss of the DCMs 2p-1-2p-k, the CPL3p, and the DCM 5p. The optical wavelength multiplex signal λ1-λk output from the AMP 6p is input to an optical band-pass filter 20 having a predetermined fixed center wavelength and band width.
Meanwhile, in the optical wavelength dividing device shown in FIG. 6, an optical wavelength multiplex signal λ1-λk is input to a BPF 21p. The optical wavelength multiplex signal λ1-λk output from the BPF 21p is collectively compensated for dispersion by a DCM 13p and amplified by an AMP 14p to compensate for the insertion loss of the DCM 13p. The optical wavelength multiplex signal λ1-λk output from the AMP 14p is divided in accordance with the wavelength by an SPL 15p, compensated individually for dispersion by DCMs 17p-1-17-k, and received by ORs 18p-1-18p-k. 
However, the optical band-pass filter of the block wavelength band has a fixed center wavelength and band width. Therefore, it has been impossible to change the combination of a center wavelength, a band width, and a number of divisions even when there is a more optimal combination of them in the block wavelength band depending on the transmission distance and the transmission fiber characteristics of a transmission system. A technique in which a signal laser is generated by a light-emitting diode by extracting a certain wavelength from the output of the light-emitting diode with a filter is disclosed in Japanese Unexamined Patent Application Publication No. 03-233425. However, it is not the one to which a technique to change the center wavelength and the band width of an optical band-pass filter according to an optical wavelength band to be transmitted within an optical wavelength multiplexing device or an optical wavelength dividing device can be applied.
Furthermore, in a case where an additional block wavelength band is provided, if the device receives an input from an optical wavelength multiplexing portion of another device that does not conform to the device specifications in terms of wavelength, optical power level, or the like, that input could have an adverse effect on the entire transmission system. Because any signal within the wavelength band can pass through it without blocking an improper signal. Furthermore, since an improper connection also has not been notified, the detection of the occurrence of malfunction has been often delayed, and a lot of time has been required to find out the cause of the malfunction.
An exemplary object of the present invention is provided an apparatus and a method of controlling the apparatus to equip an optical wavelength dividing multiplexing device with a variable optical band-pass filter, and to change the center wavelength and the band width of an optical-band pass filter according to an optical wavelength band to be transmitted.